Spatial Extent, Timing, and Causes of Channel Incision, Black Vermillion Watershed, Northeastern Kansas

The Black Vermillion River (BVR) (watershed area = 1310 square kilometers) contributes runoff and sediment into Tuttle Creek Lake, a large federal reservoir (volume = 327 million cubic meters) northeast of Manhattan, Kansas. Tuttle Creek Lake, completed in 1962, is filling with sediment faster than other federal reservoirs in the region. The lake's conservation pool is about 40 percent full of sediment and is predicted to fill by 2023. Debate rages over the relative contribution of sediment from upland sources (largely croplands and pasture) versus channel incision. Our study determined the sediment production in BVR from channel incision, which in some places exceeds six meters. The spatial extent, timing, and causes of channel incision had not been investigated previously. We will report findings based on a watershed-wide survey of several hundred channel cross-sections repeated at sites that were surveyed 45 years ago by the Soil Conservation Service. In addition, the stage of channel evolution was evaluated using the survey method of Simon and Rinaldi (2006), modified from Simon and Hupp (1986).

Channelization has reduced channel length by 24 percent in the North Fork of BVR, 26 percent in the upper main stem of BVR, and 12 percent in lower BVR. Channelized reaches are deeply incised. The spatial pattern of incision was also related to land cover, riparian vegetation, drainage area, and geology. Upper Permian limestones and shales are dominant bedrock types in the BVR watershed. Bedrock limits channel incision in the South Fork of BVR. However, bedrock is overlain over most of the watershed by Kansan age glacial till and loess, where incision prevails and is related to upland land cover, riparian vegetation, and drainage area. Our study is part of a larger effort that will compile a sediment budget for all sources in the watershed.